Olefin polymerization process in the presence of a ziegler-natta type catalyst modified with tributyl phosphite



United States Patent 3,264,277 OLEFIN POLYMERIZATION PROCESS IN THE PRESENCE OF A ZIEGLER-NATTA TYPE CATALYST MODIFIED WITH TRIBUTYL PHOSPHITE De Loss E. Winkler, Orinda, and George W. Hearne, Lafayette, Calif., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware N0 Drawing. Filed Apr. 27, 1964, Ser. No. 362,988 3 Claims. (Cl. 26093.7)

This application is a continuation-in-part of our copending patent application Serial No. 808,956, filed April 27, 1959, now US. Patent No. 3,147,238.

This invention relates to improved methods for the polymerization of alpha-olefins. More particularly, it relates to improved methods for the polymerization of alpha-rnonoolefins whereby products of improved quality are obtained.

It. is now well known that polymers of alpha-olefins may be prepared at low temperatures and'pressures in the presence of certain catalyst compositions. Such processes are conducted at temperatures ranging from about room temperature to about 150 C. .and pressures below about 500 pounds per square inch (psi). The catalysts are designated in the art generally as Ziegler catalysts or low pres-sure catalysts. Such catalysts are capable of polymerizing alpha-olefins, as ethylene, butene-l, propene, styrene and other alpha-olefins.

The present invention rel-ates to improved methods of producing polyethylene, polypropylene, polystyrene, and other polymers of alpha-olefins. It also relates to the polymerization of mixtures of such olefins to produce copolymers. As the technology as it relates to the polymeriaztion of various alpha-olefins by the use of low pressure catalysts is substantially the same for all, this invention will be described as it relates to the production of certain homopolymers but it will be understood that the invention is of general application to the polymerization of alpha-olefins and copolymers thereof using the low pressure catalysts.

The so-called low pressure catalysts which are utilized in the processes of this invention be selected from the following two groups, designated A and B; they are used, according to this invention, with an additional component which will be described hereinafter.

A. The reaction product of (1) a compound of a transition metal selected from the group consisting of titanium and vanadium with (2) a compound of the formula R R AlX wherein R and R each are hydrocarbon groups and X is halogen;

B. The reaction product of (l) a compound of a transition metal selected from the group consisting of titanium and vanadium with (2) aluminum trialkyl.

It is known that the low pressure polymerization of olefins such as propylene produces polymer-s that are designated in the art generally as crystalline polymers. These crystalline polymers are distinguished from amorphous polymers not only by their structural formula but also by their respective physical properties. The solid product of any given polymerization, e.g., of propylene, using low pressure catalyst and conditions is generally found to contain both crystalline and amorphous components. Analytical methods to determine the degree of crystallinity 3,264,277 latented August 2, 1966 are available. It is found that with increasing cryst-allinity the physical properties become increasingly more desirat a higher temperature without loss of crystalline content of the polymer. Other objects will become apparent from the detailed description of the invention.

These and other objects are accomplished in the method for the polymerization of alpha-olefins at temperatures below about C. and pressures below about 500 psi by the improvement which comprises conducting the polymerizatilon in the presence of a low pressure catalyst and a minor amount of a hydrocarbyl ester of phosphorous acid. The degree of improvement in the crystalline content of the polymer and/or process conditions will vary, depending on a number of factors as will appear more fully hereinafter.

It has been found that addition of a selected amount of tributy-lphosphite is particularly advantageous when certain preferred low pressure catalysts are employed. One of these is the novel catalysts described in US. 2,971, 925 to Winkler et al. The catalyst compositions of this invention is the reaction product formed by the steps comprising (1) reacting hydrocarbon solutions of aluminum triethyl and titanium tetrachloride in a mole ratio ranging from about 0.1:1 to less than 0.4:1 at elevated temperatures until the aluminum triethyl is completely oxidized and (2) thereafter reacting the total product of (1) with a hydrocarbon solution of aluminum diethyl chloride in an amount to give a total aluminum to titanium mole ratio of at least 1:1. The resulting product is a polymerization catalyst for alph-a-monoolefins and is capable of producing polymer having improved physical properties. This is particularly the case as it relates to the polymer of propylene.

A second preferred catalyst is the reaction product which is formed by the steps comprising (1) reacting hydrocarbon solutions of aluminum triethyl and titanium tetrachloride in a mole ratio ranging from about 0.1:1 to less than 0.421 at elevated temperatures until the aluminum triethyl is completely oxidized and (2) thereafter reacting the total reaction product of (1) with a hydrocarbon solution of aluminum triethyl in an amount to give a total aluminum to titanium mole ratio of at least In the preparation of these particular preferred types of catalysts, the order of reaction is critical as well as the amount of the specific catalyst components. The only substantial latitude permitted in the preparation of the preferred types of catalysts is in the heat treatments and in the concentrations of the components in the hydro carbon solvent.

In vthe first step ofthe preparation of either of the preferred types of catalysts, :the reaction between tetrachloride and aluminum triethyl eifects a reduction of mole'of the titanium tetrachloride; there must not be 0.4 or more moles, of the aluminum triethyl per mole of the titanium tetrachloride.

Hence the reaction in the first step between aluminum triethyl and titaniumtetra chloride must be in an aluminum triethyl to titanium tetrachloride mole ratio of less than 0.4 to 1. Theminimum :ratio is 0.l to 1. In the more-preferred procedures the mole ratio is between 0.2 0.33:1 as these ratios ul-.

timately produce the best :combination of ip ;)lymeriz-a-v "tion rates, conversions and percentage-s of linear polymer The reaction between titanium tetrachloride and a1um1-;

numtriethyl is carried out at elevated temperatures for :a period of time sufficient to oxidize ;all of the aluminum triethyl. The'time is influenced by the temperature; heat-' ting for 20 minutesat 80" C.'is suggestedas a'min'irnum' while heating for=2 hours at 80 C.'is particularly suitable;

.A rather surprising finding is that polypropylene of a substantially higher crystallinity is obtained if the heating .is carried out for periods of time substantially in excess of the minimum'required to oxidize the aluminum triethylg No explanation is ofieredfor this phenomenon other than tov :surmise thata different catalyst intermediate, which has not been identified, is formed by the longerheattre-atjment.

The initialreaction between titanium tetrachloride and aluminum triethyl is carried-out with thesereactants in;

solution with hydrocarbon solvents as pentane, isopentane, heptane, octane .and the like. The solutions of titanium tetrachloride:andaluminum triethyl are prepared, and.

measured amounts of each solution are mixed together togi vef.the desired aluminum to titanium mole ratios which range from less than 0.4.1 to about 0.121. Thehydrocarbon solutions of the catalyst components may 'be of any concentration; solutions containing 100-millimoles of reactant per liter of solvent are found-to be convenient for subsequent metering. A surprising finding is that advantages in'the ultimate polymer are'obtainedqas the. concentrations of the components in: the solvent are increased.

The reaction between titanium tetrachloride and aluminum triethyl at elevatedtemperatures terminates the first step of. the catalyst preparation. At this point the reaction mixture comprises a solid suspension in'the hydrocarbondiluent and the totalmixturehas a brown orv :purple color, depending on the -Al/Ti.: ratio and the heating time and temperature.

The second step of the preparation of the improved catalysts of US. 2,971,925 requires adding to and reacting with the total mixture prepared in step 1) aluminum,

diethyl chloride which is contained in solutionwith a hydrocarbon solvent. The amount of the aluminumdiethyl chloride added may vary a great deal with the a total aluminum to. titanium mole ratio-of- 1:1. More tetrachloride selected in .the first step; Any amount greater than theminimum is suitablebut large excesses, say in the order of 10 moles, are uneconomical and wasteful. In the preferred procedure, aluminum diethyl chlo- I ride is added in an amount tov give a total aluminum to j-titanium mole ratio ranging from about 2:1 to about 6: 1. After the aluminum diethyl chloride is added, the; total mixture, which is brown in color, is agitated briefly to "reduce the titanium tetrachloride completely. It is; not' "necessary to cool or heat the mixture to which the alumiof compounds added to the reaction mixture.

num diethyl chloride is added and the; catalyst will be.

ferred type of catalyst requires adding to and reacting,

with the total mixture prepared. in; step (1) aluminum triethyl; which is contained in solution in a hydrocarbon solvent. The 'amountof aluminum triethyl that is; added may vary, provided thatait is at. least sufiicient to provide a total. aluminum: to titanium ratio-tof 1:1.. More .preferred, ihowevenl the aluminumtriethyl is added inexcess of the ,unreacted titanium tetrachloride: of, the vfirst step. Thus, the minimum dependsentirely on the mole ratio of the aluminum rtriethyl and titanium tetrachlor'ide? selected in thefirst step. Any amount greater than the'minimum is suitable but largeexcesses, say of therorder-of 10 moles, are ,uneconomicalandwasteful. In the preferred procedure, aluminum triethyl is added; in amount to give a total aluminum to titanium mole ratio ranging from about 2:1 to about 6:1.

After the second portion of aluminum triethyl is added, the total mixture is agitated 'briefiyto complete the reduc-. tion of the titanium tetrachloride: The mixture rapidly turns from brown to black, the:. ultimate reaction product Thesuspensiom-if permitted. to stand-fora while, will I Accordingly, before being used, it should be agitatedinorder t-o-produce .a homogeneous product.

begin to settle..

which sis:used as a catalyst.

An additive .ofthisinvention :ismost suitably added to the solventor: vessel to which the catalyst components are added for. carrying out the polymerization reaction- In the polymerizationrof alpha-olefins with active low pressurecat'alysts; git is often found that the content of linear polymerinthe total product is undesirably low. It has also been-found that in some case's the reaction is .very sensitive to the reaction temperature reaction rate. is morerapid, atthe higher temperatures In a study directed to finding methods for increasing the proportion of the vlinear component: in low pressure polymer, experiments were made withv a large :number In some cases it'was found that the additive actually lowered the content of linear polymer in the: product. In, other-cases only relatively small improvements were obtained However, additives;accordingto this invention were found.

to provide outstandingly good improvementsinthecontent of linear polymer in the product; their use permits increasing. (the ;reaction temperature in the case of the catalyst of U.S. 2,971,925 while maintaining .a .high ICOI1- tent of, linear polymer in the reaction product.

Additivesto be used according to this invention arethe hydrocarbyl esters of phosphorous-acid (H PO These compounds have the general formula (ROhPiwherein R,

represents. a hydrocarbyl group ;free of terminal olefinic double bonds, preferably of from .one to twelve carbon:

Itt is not necessary to cool'or heat the.

For example, when using the zcatalyst-of U.S.: 2,971,925, the content of linear polymer, in the productis quite high when the, re-. I action temperature is. about 50 Cr, but is much lower. when the reaction is. carried out at :higher temperatures, upto It is desirable, however, .to operate at. :the higher temperatures in;this range, 'i.a.,. because the phosphite, tri-cyclohexylphosphite and the like. Although more complex compounds, e.g., those having mixed hydrocarbyl groups (butyl, di-isoamylphosphite, di-isopropyl-nbutylphosphite, butyl-diphenylphosphite) or those having involved hydrocarbyl structures, can be employed to give the desired effect, it is preferred for practical reasons to use commercially available compounds such as tributylphosphite, triethyl-, triphenylor -tris(2-ethylhexyl)phosphites and the like.

The quantity of the added phosphites preferably ranges from 1 to 33 mole percent of the combined atomic proportions of metal in the catalyst. More preferred, the quantity ranges between 2 and mole percent. As the quantiy of the added compound which is needed Will vary depending upon a number of considerations, such as the purity of. the olefin feed, the purity of the catalyst, the molecular weight desired and the like, it is preferred to first ascertain the quantity of the additive which it is most advantageous to add. This may be accomplished by an initial trial wherein a polymer is first formed without the addition of the additive; this is taken as the standard. Thereafter polymerization is conducted with, say 2, 5, 10 and 20 mole percent of the selected compound, calculated on the atomic porportion of the combined metals represented by the known amount of catalyst components of known concentration. It will be found that the stereospecificity of resulting polymer, as measured by percent insoluble, increases With increasing additive concentration. However, when increasingly larger amounts of additive are used, reaction rate begins to slow down significantly, and this usually sets the upper limit of suitable additive concentration.

The polymerizations of alpha-monoolefins according to this invention are suitably conducted in agitated pressure vessels under conditions that exclude air and other atmospheric impurities, particularly moisture. The vessel, after purging with an inert gas, is charged with a quantity of hydrocarbon solvent and a selected amount of an additive of this invention. The desired amount of catalyst is added and thereafter the monomer to be polymerized is charged to the vessel and the polymerization begins. At first, the temperature within the reactor will rise due to an exotherm so that cooling may be supplied initially in order to maintain any desired polymerization temperature, which in all cases should be less than about 100 C. and more preferably from about 40 to 80 C. The pressures are not critical and may be autogenic pressures which will vary depending upon the quantity of the solvent in the reactor, the nature of the monomer to be polymerized, the temperatures, and the like. In batch operations, the polymerization may be terminated when monomer is no longer absorbed, as indicated by a suitable pressure gauge. In continuous operations the polymerization mixture passes through a continuous reactor of any suitable design and the polymerizations in such cases are adjusted by the residence time, which may be determined by a few preliminary runs at the particular concentrations, temperatures, pressures and the like that are adopted. After the polymerization is complete the polymer is recovered as a slurry of the solid polymer in hydrocarbon dilution and a simple filtration is adequate to separate the polymer from the solvent. Thereafter the polymer may be washed a few times in order to separate catalyst residues. Further treatment may be undertaken as will be understood from the prior art.

The recovered polymer will be found, generally, to have a rather high molecular weight as indicated by intrinsic viscosity determinations in decalin at 150 C. For some applications the molecular weight may be too high and polymer of controlled molecular weight may be obtained by conducting the polymerization in the presence of various additives which reduce the molecular weight. The more effective additives for this purpose include hydrogen and zinc diethyl. In addition to these and the additives of this invention, other additives which serve other functions may be present during the polymerization. The additives, should they be used in the polymerization, are fed into the reactor before or during the polymerization and the amounts that are used will vary depending on the specific additive and the molecular weight of the polymer that it is desired to produce.

The alpha-monoolefins which can be polymerized according to the process of this invention include the normal aliphatic l-olefins ethylene, propylene, l-butene, l-pentene, 1-hexene, l-heptene and l-octene, or mixtures thereof; branched monoolefins having a terminal double bond, such as 3-methylpentene-l, 4-methylpentene-l, 3-ethylhexene-l, and the like; and styrene and alkyl-substituted styrenes. Preferably the olefins have from two to eight carbon atoms per molecule. Feeds containing a single suitable olefin or a combination of two suitable olefins may be employed.

Although it is possible to use a technical grade of alpha-olefin containing the normal impurities it is generally preferred to use a purified olefin feed; Also, it is preferred to use a catalyst prepared from high-purity components as well as hydrocarbon diluents which are relaatively free of impurities. The total quantity of impurities in the alpha-olefin to be polymerized is preferably less than 0.003% by weight. This may be illustrated for example in the case of ethylene wherein representative impurities amount to about 0.000l% by weight of acetylene, 0.0015% by weight of oxygen and about 0.0005% by weight of carbon monoxide. The various reactants may be purified in any suitable manner. Thus, for example, the olefin feed my be treated with .ammoniacal cuprous chloride or hydrogen in order to decrease or remove acetylene. If desired, an acid such as sulfuric acid may be employed to treat the olefin and the solvent. This is conventionally accomplished by employing dilute acid for treating the alpha-olefin and a more concentrated acid for treating the solvent and then distilling over calcium hydride.

In the examples and tables that follow, the intrinsic viscosity (I.V.) of a polymer is determined from measure ments of its specific viscosity in decalin at 150 C. and the insolubles content is determined by the soxhlet extraction of polymer in isooctane at its boiling point for 6 to 7 hours, using an extraction cycle of approximately 4 minutes.

Example I This example illustrates the improvement obtained when additives of this invention are included in the reaction mixture for the preparation of polypropylene by contact 'of propylene with the above-described second preferred (black) catalyst.

A catalyst is prepared by mixing in a dry nitrogen atmosphere a hydrocarbon solution of 10 millimoles (mrnoles) of TiCl (100 ml.) with 3.6 mmoles of aluminum triethyl (36 ml.) and reacting-for 2 hours at C. To this there is then added 10 mmoles of aluminum triethyl and heating continued for 1 hour at 80 C. This catalyst plus additional aluminum triethyl is used to poly- -merize propylene in separate experiments carried out in 'glass bottles. To scalable bottles of 270 ml. capacity there are added a total of 5.4 mmoles of aluminum triethyl and 0.78 mmoles of titanium chloride, prepared as above, per bottle. A desired amount of a particular additive is added and about 20 g. of propylene is then dissolved in each bottle. The bottle is capped and tumbled at the rate of 20 r.p.m. in a 50 C. water bath for about 17-20 hours. The resulting polymer slurry is then added to an equal volume of ethyl alcohol to precipitate the polymer. After filtering, washing and drying the total polymer is weighed and its I.V. and content of insolubles determined.

The results of a number of experiments carried out in this manner are shown in Table 1.

TABLE 1 Additive Product Propylene Run N o. Conversion, Percent Name Milli Percent Weight I.V.

moles Insoluble None--- 100 '73 4.0

Tribntylphosphite 0. 5 98 80 do 1. O 98 781 6. 6

Acetone 1. 5 95 67 4. Q,uinoline 1. 97 73 Phenyl isocyanate 1. 5 95 73. 4. l- Propionaldehyde 1. 5 95 v 68 I Run .1 shows typical values ofpercent insoluble and I.V. obtained with the particular catalyst employed in this series of experiments when no additive is present.

Runs 2-3 are successful runs using tributylphosphite. The additive served to substantially increase the linear content of the polymer (as indicated by percent insoluble). It also caused some "increase in the molecular Weight (as indicated byincreased I.V.); this effect is not steel, stirred autoclave, there is added a desired amount of an additive; propylene is then added at an average pressure of p.s.i.g. After. 4.5 hours the reaction 'is. stopped by the addition of alcohol and the polymer T63, covered as previously described.

A series of runs are made .in this; manner, with and iwithout additives, and at various temperatures. The results are shown in Table 2.

TABLE 2 necessarily desirable, but can be suppressed, if it is desired to do so,'by addition of certain materials during the .re,,.

action, e.g., hydrogen.

Runs 4-7 show that various other materials, used in 2 corresponding concentrations, did not resultin polypropylene ofsubstantial-ly improved crystallinity.

Example 2 Runs 2 and 3 are repeated, substituting for-tributylphosphite triethylphosphite, trioctylphosphite, .and triphenylp'hosphite; Similar improvements in polypropylene 1 crystallinity are obtained.

Example 3 A catalyst is prepared by mixing under a nitrogen at-' mosphere a hydrocarbon solution of 10 mmoles of TiCl (100 ml.) with 3.6 moles of AlEt (3-6 ml.) and reacting l 2 .hours at C. This-mixture is then centrifuged, the supernatant liquid decanted, and 10 mmoles (100 ml.) of

AIEt Cladded and the mixture heated another hour at 80 C. This catalyst is then added I04 liters of purified isooctane containing 80 moles of AlEt Cl. To various amounts of this reaction mixture, contained in a stainless Runs 8,10 illustrate. the effect of increasing the reactiontemperature from 50 to C. in the absence of an additive. The reaction rate .is increased, :but both the proportion of linear polymer :and themolebular; weight of the. polymer; are substantially; decreased; Run '11 shows that 'addition of tributylphosphite to a'rnixture which is reacted at 70 C. results in a polymer havinga higher insolubles content .thanspolymer obtained at 50 C; in the: a'bsenceof an additive, andresultsyin some increase in the molecularaweight. The reaction rate is what would be found at 55". C; inthe absence. of additive.v However,

a still higher temperature can be employed with this addi tive to improve the reaction rate without substantial decrease in linearity of the polymer.

Example ;4

Catalysts are prepared and reactions carried out substantially as in Example 3. In the first step of the cata lyst preparation, 3.0 mmoles of AlEt is usedinstead of 3.6. The catalyst used in Runs 15-18 is used without separationof solids by centrifuging. In the. runs illustrated in Table 3 it is shown that tributylphosphiteg:used;

9 in the presence of hydrogen, results in a product whose linearity is high while its molecular weight is lower than that produced in the absence of both additive and hydrogen. For the latter value, see Runs 8-10, in Ex- 10 having up to ten carbon atoms are most suitable for the processes of this invention.

We claim asour invention: 1. In the process of polymerizing propylene which comample 3. 5 pnses contacting propylene with a catalyst prepared by TABLE 3 Run No. 12 13 14 15 16 17 18 AlEtgCl (millimoles) 80 80 80 80 80 80 80 TiCl (millirnoles) 16 8 16 18 18 9 9 Additive (Tributylphosphite) mi1limoles 13 13 6. 5 3 H (m1 at. room conditions) 250 500 500 500 500 500 500 Temperature, C 50 70 70 50 70 70 70 G. Polymer/g. TiCl /hr 58 121 66 47 6O 77 119 Percent Weight Insoluble- 93 88 93 92 95 93 89 I.V 3. 5 2.3 2. 9 3.0 2. 9 2. 7 2. 3

0.15 2. 72 4, 490 4,010 4, 240 2, 680 740 2 700 Flexural Stiffness, p.s.i 158,000 127,000 139,000 141, 000 150,000 149,000

Example 6 A series of runs are carried out in a manner similar to those of Example 1, but employing as catalyst vanadium trichloride and aluminum triethyl.

In Runs 19-22, 200 ml. of solvent containing 0.4 mm-o-les of VCl and 5.4 mmoles of aluminum triethyl, are placed in sealable bottles. A desired amount of additive is added to each bottle, about 20 g. of propylene dissolved in the solution and the bottle sealed and treated as in Example 1.

The results of the experiments are shown in Table the sequence of steps comprising (1) reacting hydrocarbon solutions of aluminum triethyl and titanium tetrachloride in a rnole ratio ranging from about 0.121 to less than 0.4:1 at elevated temperatures until the aluminum triethyl is completely oxidized and (2) thereafter reacting the total product of (l) with a hydrocarbon solution of aluminum triethyl or aluminum diethyl chloride, in an amount to give a total aluminum to titanium mole ratio of at least 1:1; the improvement which comprises carrying out said contact in the presence of an effective amount 4. in the range from 2 to 10 mole percent, based on the com- The results of Table 4 show a substantial improvement in wt. percent insoluble, indicating improved crystal-linity of the polymer.

Example 7 Polymerizations of bu-tene-l and of 4-methylpentene-l, carried out in the manner of Example 3, show a substantial increase in crystallinity of the resulting polymer when tributylphosphite or triisoamylphosph-ite are employed. as additives.

From the foregoing it will readily be appreciated that the processes of this invention are capable of many modifications of the processing techniques, most of which are known in the low pressure polymerization methods of alpha-olefins. Thus, for example, the polymerization may .be conducted with or without catalyst supports. It will be obvious that the method of addition of the additives of this invention may be varied as, for example, by the intermediate or irregular addition of the additive in a continuous or batch process. Further, the processes of this invention are equally suitable for controlling the polymer linearity of polymerized .alpha-olefins other than those shown in the examples. However, alpha-olefins bined atomic proportions of metal in the catalyst of tributyl phosphite.

2. In the process of polymerizing propylene which corn prises contacting propylene with a catalyst prepared by the sequence of steps comprising (1) reacting hydrocarbon solutions of aluminum triethyl and titanium tetrachloride in a mole ratio ranging from about 0.1:1 to less than 0.4:1 at elevated temperatures until the aluminum tniethyl is completely oxidized, (2) separating the result ing solid reaction product, and (3) thereafter reacting the total product of (l) with a hydrocarbon solution of alu-, minum triethyl, in an amount to give a total aluminum to titanium mole ratio of at least 1:1; the improvement which comprises carrying out said contact in the presence of an effective amount in the range from 2 to 10 mole percent, based on the combined atomic proportions of metal in the catalyst of tributyl phosphite.

3. In the process of polymerizing propylene which comprises contacting propylene with a catalyst prepared by the sequence of steps comprising (1) reacting hydrocarbon solutions of aluminum triethyl and titanium tetrachloride in a mole ratio ranging from about 0.1:1 to less 1 1 1 2, than 0.4:1 at elevated te-meperatures until the aluminum References Cited by thevExaminer triethyl is completely oxidized, (2) separating the result- UNITED STATES PATENTS mg solid reaction product, and (3) thereafter reacting the 7 total product of (1) With a hydrocarbon solution of alu- 2,886,561 5/1959 Reynolds etlal 26044-9 minum diethyl chloride, in an :amount to give a total 5 2,956,991 10/1960v Coover et a1? 6 aluminum to titanium mole ratio of at least 1:1; the im- 3,032,510 5/ 19627 Tofnqllistei provement whichcomprises carrying out said contact in 3,186,977 6/1965" Coover et the presence of an effective amount in the range from 2 a a. to 10 mole percent, based on the combined atomic-pro JOSEPH SCHOFER Prlmm'y Exammer" portions of metal in the catalyst of tributyl phosphiter 10 M. B. KURTZMAN; Assistant Examiner. 

1. IN THE PROCESS OF POLYMERIZING PROPYLENE WHICH COMPRISES CONTACTING PROPYLENE WITH A CATALYST PREPARED BY THE SEQUENCE OF STEPS COMPRISING (1) REACTING HYDROCARBON SOLUTIONS OF ALUMINUM TRIETHYL AND TITANIUM TETRACHLORIDE IN A MOLE RATIO RANGING FROM ABOUT 0.1:1 TO LESS THAN 0.4:1 AT ELEVATED TEMPERATURES UNTIL THE ALUMINUM TRIETHYL IS COMPLETELY OXIDIZED AND (2) THEREAFTER REACTING THE TOTAL PRODUCT OF (1) WITH A HYDROCARBON SOLUTION OF ALUMINUM TRIETHYL OR ALUMINUM DIETHYL CHLORIDE, IN AN AMOUNT TO GIVE A TOTAL ALUMINUM TO TITANIUM MOLE RATIO OF AT LEAST 1:1; THE IMPROVEMENT WHICH COMPRISES CARRYING OUT SAID CONTACT IN THE PRESENCE OF AN EFFECTIVE AMOUNT IN THE RANGE FROM 2 TO 10 MOLE PERCENT, BASED ON THE COMBINED ATOMIC PROPORTIONS OF METAL IN THE CATALYST OF TRIBUTYL PHOSPHITE. 